1. Field of the Invention
The present invention relates to oil well drilling and more particularly relates to directional drilling. Even more particularly the present invention relates to the use of an improved two-part locking slot with a two-section "sub" which operates in combination with, for example, a conventional turbodrill wherein in the invention the "sub" movably shifts from a first position in which the turbodrill is substantially axially aligned with the drill string, to a second or "bent" position whereby a deflection is created between the drill string and the turbodrill of a desired degree.
2. General Background
Although wellbores are normally planned to be drilled vertically, many occasions arise when it is necessary or advantageous to drill at an angle from the vertical. Controlled directional drilling, as it is referred to in the art, makes it possible to reach subsurface points laterally remote from the point where the drill bit enters the earth. Some examples of the use of directional drilling are inaccessible locations (such as under rivers or like bodies of water when the drilling begins on land), salt dome control, relief well control, edgewell control, fault plane control and property line control. Additionally, directional drilling is employed in offshore applications where all the drilling necessarily must take place from a fixed platform in a location in the offshore waters. A further application of directional drilling is seen when obstructions prevent a substantially vertical well direction.
One method of directionally drilling wells is a whip-stock method. Another, very popular, method employs a turbodrill in combination with a bent sub assembly. The turbodrill is a conventional device which uses fluid that is pumped under pressure through the center of the motor directed downwardly through void areas between a "rotor" and the rubber-lined spiral passageway of an outer "stator". In order for the flow to occur, the rotor is displaced and turned within the stator by the pressure of the fluid column, thus powering the connecting rod, a hollow drive shaft, and finally a conventional bit sub at the end of the tool.
One such manufactured turbodrill is the "Dyna-Drill" which was introduced in or about 1964. Operation and use of the "Dyna-Drill" for directional drilling can be found in "Dyna-Drill Handbook" (second edition) distributed by Dyna-Drill Division of Smith International, Inc., P. O. Box 327, Long Beach, Calif. 90801. In drilling, a "sub" is a short threaded piece of drill pipe used to connect together parts of the drilling string which could not otherwise be screwed together because of difference in thread size or design.
In the case of directional drilling, the "sub" is bent to produce the desired angle between the lower portion of the drill string (a non-magnetic survey collar normally being the lowermost portion of the drill string which attaches to the sub) and the turbodrill, "Dyna-Drill", or the like which attaches to the opposite end of the sub (this general arrangement is illustrated in FIG. 1 of applicant's U.S. Pat. No. 4,220,214, issued Sep. 2, 1980, wherein a conventional permanently bent sub if the prior art is illustrated). In U.S. Pat. No. 4,303,135, entitled "Directional Drilling Sub", a variable angle adjustment for a directional drilling sub is disclosed. U.S. Pat. Nos. 4,220,214 and 4,303,135 are hereby incorporated herein by reference.
The use of a fixed or non-shifting bent sub requires that the drill string be lowered into the well from the surface with the bent sub creating a kink in the lowermost portion of the drill string, which kink causes problems in lowering the turbodrill into the well. Since the turbodrill is of some length (a length of thirty feet being exemplary), even a small degree of being in the sub can create a relatively large eccentricity in the drill string.
Many patents have been issued which are directed to the problem of directional drilling. Most of these patents provide structures which are directed to solving the problem of effecting the direction of drilling itself, but do not completely and satisfactorily solve the problem of lowering the turbodrill and bent sub in the "kinked" position into the well or lowering it in an "unkinked" position and then allowing for later deviation when "down in the hole".